A lithography technique with an ArF excimer laser as a light source is used for forming a fine pattern in a semiconductor manufacturing process. With the miniaturization of the pattern, the lithography is performed in the vicinity of a resolution limit in which the fine pattern of a size of a fraction of a wavelength of the ArF excimer laser is formed. An Optical Proximity Correction (OPC) technique for correcting a mask pattern shape or an exposure light source shape is essential for the lithography which is in the vicinity of the resolution limit in consideration of a proximity effect of the light. For optimization of the correction, it is necessary to measure a fine resist sample actually prepared by transferring a mask pattern and, to evaluate a deviation from a design, and to correct the mask or the light source shape.
For measurement of an outline of a pattern shape of the fine resist sample, a scanning electron microscope (SEM) is used. Brightness in an edge portion of the pattern is strong in a SEM image of a sample obtained by using the SEM. The portion in which the brightness is strong is referred to as a white band and it is possible to measure the outline of the pattern shape of the sample by extracting the white band as a line segment. Furthermore, it is possible to extract the outline with high accuracy by determining a point (edge point) configuring the outline based on a brightness profile in the vicinity of the white band.
However, the outline extracted from the SEM image by such a method is affected by contraction (shrinking) of the resist or charging of a resist surface by electron beam irradiation when observing the SEM. As a method to deal with such a problem, a method for correcting fluctuation of a SEM bias due to the charging by replacing the brightness profile of a correction target region is disclosed in PTL 1.
Furthermore, there is a problem that the outline is lost when extracting the white band as the line segment in the SEM image in which noise is strong or a large error occurs in a position of the edge point in the image in which contrast of the white band is weak. As a method to deal with such a problem, a method for appropriately connecting a lost portion of the outline is disclosed in PTL 2 and a method for increasing the reliability of the outline by configuring the outline excluding the edge point if a degree of separation of the brightness is small in the brightness profile in the vicinity of the edge point is disclosed in PTL 3.